In many cases it is important that medicaments be administratable by an unskilled individual such as the patient himself by injection. For this reason so-called automatic syringes have been developed which, upon positioning against the skin, can be triggered so that the needle is automatically driven into the skin and medicament contained in the instrument is driven through the needle into the subcutaneous tissues.
Such syringes are desirable for patients suffering from allergies, various cardiovascular disorders and certain types of diabetes which may require immediate application of the injectable medicament so that there is no time for the patient to reach a skilled medical practitioner.
Probably the most significant of these disorders from the point of view of immediacy, is anaphylactic shock which can require an injection of epinephrine (adrenaline) without delay.
It is known to provide an automatic syringe which comprises a cylindrical barrel adapted to receive an ampule containing the medicament to be administered and which can be formed from a synthetic resin material and provided at its end turned toward the patient, with a fitting enabling a needle to be attached thereto so that the body of the ampule constitutes, simultaneously the carrier of the needle and the guide or support structure therefor.
In addition to the ampule, the barrel can be provided with a plunger which can be spring biased so as to drive the needle into the skin and expel the medicament from the ampule through the needle, a device for holding the plunger against the action of the spring until release is desired and a safety mechanism to prevent undesired discharge of the contents of the ampule.
In practice, the system in which the ampule body of molded synthetic resin constitutes the support for the needle and defines the wall of the container for the medicament has proved to be disadvantageous at least for certain medicaments such as adrenaline.